Positive electrode active material layer, lithium ion battery, and method for manufacturing positive electrode active material layer

Abstract

To provide a positive electrode active material layer which can improve battery capacity, a lithium ion battery comprising such a positive electrode active material layer, and a method for manufacturing such a positive electrode active material layer.SOLUTION: A positive electrode active material layer 20 of the present disclosure includes a positive electrode active material 21a and a lithium alloy 22a of lithium and a metal element. The positive electrode active material is coated with a carbon material. The metal element has an alloying potential with lithium of 0.5 V (vs.Li / Li+) or more, and the lithium alloy is arranged on a surface of the positive electrode active material layer on a positive electrode current collector 10 side and / or on a surface of the positive electrode active material layer on a separator 30 side. A lithium ion battery 1 of the present disclosure includes a positive electrode current collector 10, a separator 30, and a positive electrode active material layer 20 of the present disclosure, which is interposed between the positive electrode current collector 10 and the separator 30.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a positive electrode active material layer, a lithium ion battery, and a method for producing a positive electrode active material layer. [Background technology]

[0002] A part of the lithium ions supplied from the positive electrode active material of a lithium-ion battery is consumed to react with the electrolyte on the surface of the negative electrode active material layer to form a solid electrolyte interface (SEI). As a result, the problem of a decrease in battery capacity occurs. Therefore, in order to make the most of the positive electrode active material, it is necessary to supplement the lithium ions consumed to form the SEI in the negative electrode active material layer, and technologies for this purpose have been developed.

[0003] For example, Patent Document 1 discloses a positive electrode for a secondary battery, which includes a positive electrode mixture layer (positive electrode active material layer) in which a positive electrode active material and a lithium-based alloy are mixed. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Special Publication No. 2021-520614 Summary of the Invention [Problem to be solved by the invention]

[0005] Even in batteries having a positive electrode active material and a positive electrode active material layer that includes a lithium alloy, the desired battery capacity may not be obtained, and therefore there is room for improvement in battery capacity.

[0006] An object of the present disclosure is to provide a positive electrode active material layer capable of improving battery capacity, a lithium ion battery having such a positive electrode active material layer, and a method for producing such a positive electrode active material layer. [Means for solving the problem]

[0007] The present inventors have found that the above problems can be solved by the following means. <Aspect 1> A positive electrode active material layer interposed between a positive electrode current collector and a separator, A positive electrode active material and a lithium alloy of lithium and a metal element, The positive electrode active material is coated with a carbon material, The metal element has an alloying potential with lithium of 0.5V (vs. Li / Li + ) or more, and the lithium alloy is disposed on a surface of the positive electrode active material layer facing the positive electrode current collector and / or a surface of the positive electrode active material layer facing the separator; Cathode active material layer. <Aspect 2> 2. The positive electrode active material layer of embodiment 1, wherein the lithium alloy forms a lithium alloy layer. <Aspect 3> 3. The positive electrode active material layer according to aspect 2, wherein the lithium alloy layer has a thickness of 1 μm or more and 20 μm or less. <Aspect 4> The positive electrode active material layer according to any one of aspects 1 to 3, wherein the positive electrode active material is an olivine type positive electrode active material. <Aspect 5> 5. The positive electrode active material layer according to aspect 4, wherein the olivine type positive electrode active material is at least one selected from the group consisting of lithium iron phosphate, lithium manganese iron phosphate, lithium manganese phosphate, and lithium cobalt phosphate. Aspect 6 The positive electrode active material layer according to any one of aspects 1 to 5, wherein the metal element is at least one selected from bismuth, antimony, and tin. Aspect 7 7. The positive electrode active material layer according to any one of aspects 1 to 6, wherein the ratio of the mass of the positive electrode active material to the mass of the lithium alloy is 3.0 or more and 15.0 or less. <Aspect 8> The positive electrode active material layer according to any one of aspects 1 to 7, wherein the thickness of the positive electrode active material layer excluding the lithium alloy is 20 μm or more and 300 μm or less. <Aspect 9> The positive electrode current collector, The separator, and A positive electrode active material layer according to any one of aspects 1 to 8, which is interposed between the positive electrode current collector and the separator. A lithium-ion battery having Aspect 10 positive electrode current collector, Separator, and a positive electrode active material layer interposed between the positive electrode current collector and the separator; A lithium ion battery having the positive electrode active material layer has a positive electrode active material and a metal element, The positive electrode active material is coated with a carbon material, The metal element has an alloying potential with lithium of 0.5V (vs. Li / Li + ) or more, and the metal element is disposed on a surface of the positive electrode active material layer facing the positive electrode current collector and / or a surface of the positive electrode active material layer facing the separator. Lithium-ion battery. <Aspect 11> A method for producing the positive electrode active material layer according to any one of aspects 1 to 8, comprising the following steps: (a) applying a first slurry containing the lithium alloy and a first dispersion medium to a substrate; (b) applying a second slurry containing the positive electrode active material and a second dispersion medium after the step (a); (c) drying and removing the first and second dispersion media to obtain a laminate; and (d) pressing the laminate; Aspect 12 12. The method of claim 11, wherein the substrate is a positive electrode current collector. Aspect 13 13. The method of claim 11 or 12, further comprising, prior to step (b), drying off the first dispersing medium to obtain a preliminary lithium alloy layer. Aspect 14 14. The method of embodiment 13, further comprising pressing the preliminary lithium alloy layer to obtain a lithium alloy layer. Aspect 15 A method according to any one of aspects 11 to 14, wherein the first and second dispersion media are the same dispersion medium. Effect of the Invention

[0008] According to the present disclosure, it is possible to provide a positive electrode active material layer capable of improving battery capacity, a lithium ion battery having such a positive electrode active material layer, and a method for producing such a positive electrode active material layer. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a schematic cross-sectional view showing an example of a positive electrode active material layer according to the present disclosure. [Diagram 2] FIG. 2 is a schematic cross-sectional view showing an example of a positive electrode active material layer according to the present disclosure. [Diagram 3] FIG. 3 is a schematic cross-sectional view of a positive electrode active material layer of a comparative example. [Figure 4] FIG. 4 is a schematic cross-sectional view showing an example of a battery according to the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, embodiments of the present disclosure will be described in detail. Note that the present disclosure is not limited to the following embodiments, and various modifications can be made within the scope of the present disclosure.

[0011] 《Cathode active material layer》 The positive electrode active material layer of the present disclosure is interposed between a positive electrode current collector and a separator, and includes a positive electrode active material and a lithium alloy of lithium and a metal element. The positive electrode active material is coated with a carbon material, and the metal element has an alloying potential with lithium of 0.5 V (vs. Li / Li +) or more, and the lithium alloy is disposed on the surface of the positive electrode active material layer on the positive electrode current collector side and / or on the surface of the positive electrode active material layer on the separator side. In the present disclosure, "the lithium alloy is disposed on the surface of the positive electrode active material layer on the positive electrode current collector side and / or on the surface of the positive electrode active material layer on the separator side" means that the lithium alloy is disposed on the surface on the positive electrode current collector side or the surface on the separator side at a higher density than in other parts, and particularly means that the lithium alloy is disposed only on the surface on the positive electrode current collector side and / or the surface on the separator side.

[0012] The present inventors considered that one of the reasons why a desired battery capacity cannot be obtained even in a battery having a positive electrode active material layer containing a positive electrode active material and a lithium alloy is that the carbon material covering the positive electrode active material reacts with the lithium alloy. Specifically, without intending to be bound by any theory, this is presumed as follows. That is, since the oxidation-reduction potential of the lithium alloy is low, it is considered that the lithium alloy reacts with the carbon material covering the positive electrode active material during the first charge, damaging the coating of the carbon material. As a result, it is considered that the adhesion between the positive electrode active material and the carbon material decreases, and the resistance increases, so that the desired battery capacity cannot be obtained.

[0013] In this regard, the present inventors have found that in a positive electrode active material layer containing a positive electrode active material coated with a carbon material and a lithium alloy of lithium and a predetermined metal element, the lithium alloy is disposed on the surface of the positive electrode active material layer on the positive electrode current collector side and / or the surface of the positive electrode active material layer on the separator side, thereby improving the battery capacity. The reason for this is presumed to be as follows, without intending to be bound by any theory. That is, it is believed that by disposing the lithium alloy on the surface on the positive electrode current collector side and / or the surface on the separator side, the contact area between the carbon material coating the positive electrode active material and the lithium alloy can be made smaller than in a state in which the positive electrode active material and the lithium alloy are mutually dispersed in the positive electrode active material layer.

[0014] Hereinafter, the positive electrode active material layer of the present disclosure will be described with reference to the drawings as appropriate. Note that the dimensional relationships in each drawing do not reflect the actual dimensional relationships.

[0015] 1 and 2, the positive electrode active material layer 20 of the present disclosure includes a positive electrode active material 21a and a lithium alloy 22a of lithium and a metal element. The positive electrode active material layer optionally includes a conductive additive and a binder. In addition, when the lithium ion battery of the present disclosure is a solid-state battery, the positive electrode active material layer optionally includes a solid electrolyte.

[0016] As shown in FIGS. 1 and 2, a positive electrode active material layer 20 of the present disclosure is interposed between a positive electrode current collector 10 and a separator 30.

[0017] 1, the lithium alloy 22a is disposed on the surface on the side of the positive electrode current collector 10. Although not shown, the lithium alloy 22a may also be disposed on the surface on the side of the separator 30. It is considered that such a configuration can reduce the contact area between the carbon material covering the positive electrode active material 21a and the lithium alloy 22a, compared to the state in which the positive electrode active material 21a and the lithium alloy 22a are mutually dispersed in the positive electrode active material layer 20 as shown in FIG.

[0018] 2, the lithium alloy 22a may form a lithium alloy layer 22 on the surface on the positive electrode current collector 10 side. Although not shown, the lithium alloy 22a may form a lithium alloy layer on the surface on the separator 30 side.

[0019] When the lithium alloy 22a is disposed on the surface on the side of the positive electrode current collector 10, it is believed that the durability of the battery is improved. This is presumed as follows, without intending to be bound by any theory. That is, ions of metal elements generated by releasing lithium ions from the lithium alloy during charging may move toward the negative electrode current collector during repeated charging and discharging, and may precipitate as simple metal elements on the negative electrode current collector. When this precipitate occurs locally, it becomes a dendrite, and when this grows and reaches the positive electrode current collector, a short circuit occurs. By disposing the lithium alloy 22a on the surface on the side of the positive electrode current collector 10, the distance between the metal element and the negative electrode current collector becomes longer than when the lithium alloy 22a is disposed on the surface on the side of the separator 30, which makes it difficult for local dendrites to precipitate, and as a result, it is believed that the possibility of the above-mentioned short circuit can be reduced.

[0020] <Cathode active material> The positive electrode active material is coated with a carbon material.

[0021] The positive electrode active material may be an olivine type positive electrode active material.

[0022] The olivine type positive electrode active material may be at least one selected from lithium iron phosphate, lithium manganese iron phosphate, lithium manganese phosphate, and lithium cobalt phosphate.

[0023] Carbon materials can improve the electronic conductivity of positive electrode active materials by coating them. In particular, olivine-type positive electrode active materials have lower electronic conductivity than ternary positive electrode active materials such as nickel-cobalt-manganese (NCM), so coating them with carbon materials is effective.

[0024] The method for coating the positive electrode active material with a carbon material is not particularly limited, but an example thereof is a method in which the positive electrode active material is coated with a predetermined organic compound, and the positive electrode active material coated with the organic compound is baked in an inert atmosphere to carbonize the organic compound.

[0025] In the present disclosure, a commercially available product may be used as the positive electrode active material coated with a carbon material.

[0026] <Lithium alloy> The lithium alloy can supply lithium ions, which can prevent the lithium ions of the positive electrode active material from being consumed in the formation of the SEI in the negative electrode active material layer, making it possible to make the most of the positive electrode active material and increasing the reversible capacity.

[0027] Metal elements that form lithium alloys have an alloying potential with lithium of 0.5V (vs. Li / Li + ) or more. This stabilizes the lithium alloy and makes it easier to handle the lithium alloy. This alloying potential is 0.6V (vs Li / Li + ) or more, 0.7V(vs Li / Li + ) or more, or 0.8V(vs Li / Li + ) or more, and 1.5V (vs Li / Li + ) or less, 1.4V (vs Li / Li + ) or less, 1.3V (vs Li / Li + ) or less, 1.2V (vs Li / Li + ) or less, 1.1V (vs Li / Li + ) or less, or 1.0V(vs Li / Li + ) or less.

[0028] Here, the alloying potential (vs Li / Li + ) is the electrode potential of the electrode reaction of formula (1) and is expressed based on the electrode potential of lithium of the following formula (2): xLi + +M+xe - ←→ Li x M (1) Li + +e - ←→ Li (2)

[0029] Alloying potential (vs Li / Li +) can be measured as the single electrode potential obtained when the alloy is immersed in a salt solution of Li.

[0030] The metal element may be at least one selected from bismuth, antimony, and tin.

[0031] The lithium alloy may be prepared by a conventional method or may be a commercially available product. The method for preparing the lithium alloy includes, but is not limited to, a method of mixing lithium and a metal element in a mortar in an inert atmosphere.

[0032] The ratio of the mass of the positive electrode active material to the mass of the lithium alloy in the positive electrode active material layer of the present disclosure may be 3.0 or more and 15.0 or less. This ratio may be 3.5 or more, 4.0 or more, 5.0 or more, or 6.0 or more, and may be 14.0 or less, 13.0 or less, 12.0 or less, or 11.0 or less. Due to the high capacity characteristics of the material itself, the lithium alloy can contribute to an increase in battery capacity even when added in a small amount as in the above range. This ratio can be appropriately designed depending on the type of positive electrode active material and lithium alloy used, etc.

[0033] The ratio of the volume of the positive electrode active material to the volume of the lithium alloy of the present disclosure may be 5.0 or more, 6.0 or more, 7.0 or more, 8.0 or more, or 8.5 or more, and may be 20.0 or less, 19.0 or less, 18.0 or less, 17.0 or less, or 16.5 or less. This ratio can be appropriately designed depending on the type of positive electrode active material and lithium alloy used, etc.

[0034] When the lithium alloy forms a lithium alloy layer on the surface on the positive electrode current collector side and / or the surface on the separator side, the thickness of the lithium alloy layer may be 1 μm or more and 20 μm or less. This thickness may be 2 μm or more, 3 μm or more, 4 μm or more, or 5 μm or more, and may be 18 μm or less, 16 μm or less, 15 μm or less, 14 μm or less, 12 μm or less, 11 μm or less, or 10 μm or less.

[0035] The thickness of the layer obtained by removing the lithium alloy from the positive electrode active material layer may be 20 μm or more and 300 μm or less. This thickness may be 40 μm or more, 60 μm or more, 70 μm or more, 80 μm or more, or 90 μm or more, and may be 250 μm or less, 200 μm or less, 150 μm or less, 130 μm or less, 120 μm or less, or 110 μm or less. The layer obtained by removing the lithium alloy from the positive electrode active material layer may be, in particular, a layer obtained by removing the lithium alloy layer from the positive electrode active material layer. In addition, in the present disclosure, a layer obtained by removing the lithium alloy or the lithium alloy layer from the positive electrode active material layer may be referred to as a layer containing a positive electrode active material (e.g., LFP).

[0036] The content of the lithium alloy in the positive electrode active material layer can be adjusted so that the lithium alloy does not form a layer or forms a layer, i.e., the content of the lithium alloy can be reduced so that the lithium alloy does not form a layer, and the content of the lithium alloy can be increased so that the lithium alloy forms a layer.

[0037] <Conductive assistant> The conductive assistant may be any known conductive assistant used in lithium ion batteries. Specifically, carbon materials such as Ketjen Black (KB), vapor grown carbon fiber (VGCF), acetylene black (AB), carbon nanotubes (CNT), carbon nanofibers (CNF), carbon black, coke, graphite, etc. may be used. Alternatively, metal materials capable of withstanding the environment during use of the battery may be used. As the conductive assistant, only one type may be used alone, or two or more types may be used in combination. The conductive assistant may be in various forms such as powder and fiber. The amount of the conductive assistant contained in the positive electrode active material layer is not particularly limited.

[0038] <binder> The binder may be any binder known in the art for use in lithium ion batteries. For example, styrene butadiene rubber (SBR)-based binders, carboxymethyl cellulose (CMC)-based binders, acrylonitrile butadiene rubber (ABR)-based binders, butadiene rubber (BR)-based binders, polyvinylidene fluoride (PVDF)-based binders, polytetrafluoroethylene (PTFE)-based binders, etc. may be used. Only one type of binder may be used alone, or two or more types may be used in combination. The amount of binder contained in the positive electrode active material layer is not particularly limited.

[0039] <Solid electrolyte> The material of the solid electrolyte is not particularly limited, and any material that can be used as a solid electrolyte for use in a lithium ion battery can be used. For example, the solid electrolyte may be a sulfide solid electrolyte, an oxide solid electrolyte, a polymer electrolyte, or the like.

[0040] Examples of sulfide solid electrolytes include, but are not limited to, sulfide amorphous solid electrolytes, sulfide crystalline solid electrolytes, and argyrodite-type solid electrolytes. Specific examples of sulfide solid electrolytes include Li2S-P2S5-based (Li7P3S 11 , Li3PS4, Li8P2S9, etc.), Li2S-SiS2, LiI-Li2S-SiS2, LiI-Li2S-P2S5, LiI-LiBr-Li2S-P2S5, Li2S-P2S5-GeS2(Li 13 GeP3S 16 , Li 10 GeP2S 12 etc.), LiI-Li2S-P2O5, LiI-Li3PO4-P2S5, Li 7-x P.S. 6-x Cl x etc.; or combinations thereof, but are not limited to these.

[0041] An example of an oxide solid electrolyte is Li7La3Zr2O 12 , Li 7-x La3Zr 1-x Nb x O12 , Li 7-3x La3Zr2Al x O 12 , Li 3x La 2 / 3-x TiO3, Li 1+x Al x Ti 2-x (PO4)3, Li 1+x Al x Ge 2-x (PO4)3, Li3PO4, or Li 3+x PO 4-x N x (LiPON), but is not limited to these.

[0042] The sulfide solid electrolyte and the oxide solid electrolyte may be glass or crystallized glass (glass ceramic).

[0043] Examples of the polymer electrolyte include, but are not limited to, polyethylene oxide (PEO), polypropylene oxide (PPO), and copolymers thereof.

[0044] <<Method for producing positive electrode active material layer>> The disclosed method for producing a positive electrode active material layer includes the following steps: (a) applying a first slurry containing a lithium alloy and a first dispersion medium to a substrate; (b) after step (a), applying a second slurry containing a positive electrode active material and a second dispersion medium; (c) drying and removing the first and second dispersion mediums to obtain a laminate; and (d) pressing the laminate.

[0045] <First slurry application step> The method of the present disclosure includes (a) applying a first slurry comprising a lithium alloy and a first carrier fluid to a substrate.

[0046] For the lithium alloy, reference can be made to the above description regarding the positive electrode active material layer of the present disclosure.

[0047] The first dispersion medium is not particularly limited as long as it can disperse the lithium alloy and does not deteriorate the lithium alloy. Examples of the first dispersion medium include alcohol, glycol, cellosolve, amine, ketone, carboxylic acid amide, phosphoric acid amide, sulfoxide, carboxylic acid ester, phosphoric acid ester, ether, and nitrile. Specific examples include ethanol, 2-propanol, methyl ethyl ketone, and N-methyl-2-pyrrolidone.

[0048] The substrate may be a positive electrode current collector. By using the substrate as the positive electrode current collector, the lithium alloy layer can be formed directly on the positive electrode current collector.

[0049] The substrate may be a separator. By using the substrate as a separator, the lithium alloy layer can be formed directly on the separator.

[0050] Examples of the coating method include metal mask printing, electrostatic coating, dip coating, spray coating, roll coating, doctor blade coating, gravure coating, and screen printing.

[0051] <Second Slurry Coating Step> The method of the present disclosure includes, after step (a), applying a second slurry comprising a positive electrode active material and a second dispersion medium.

[0052] For the positive electrode active material, reference can be made to the above description regarding the positive electrode active material of the present disclosure.

[0053] The second dispersion medium is not particularly limited as long as it can disperse the positive electrode active material and does not alter the positive electrode active material. Examples of the second dispersion medium include alcohol, glycol, cellosolve, amine, ketone, carboxylic acid amide, phosphoric acid amide, sulfoxide, carboxylic acid ester, phosphoric acid ester, ether, and nitrile. Specific examples include ethanol, 2-propanol, methyl ethyl ketone, and N-methyl-2-pyrrolidone.

[0054] The first and second dispersion media in the method of the present disclosure may be the same dispersion media. By using such a method, even when the second slurry is directly applied onto the first slurry, each slurry layer can be formed without being affected by the surface tension caused by the different dispersion media, that is, without excessive mixing of the components in the first and second slurries.

[0055] The first and second slurries may contain a binder, but if the binder in each slurry is the same, the same effect can be achieved as when the dispersion medium is the same.

[0056] Furthermore, for example, by increasing the solid content concentration of the first slurry, the viscosity of the first slurry can be increased, so that even in the case where the second slurry is directly applied onto the first slurry, the components in the first and second slurries can be effectively prevented from mixing with each other.

[0057] <Drying process> The method of the present disclosure also includes (c) drying and removing the first and second dispersion media to obtain a laminate.

[0058] The drying temperature, drying time, etc. can be appropriately designed depending on the content and boiling point of the dispersion medium, etc.

[0059] The method of the present disclosure may further include, before step (b), drying and removing the first dispersion medium to obtain a preliminary lithium alloy layer. By adopting such a method, the dispersion medium and binder of the first and second slurries may be selected without any particular limitation.

[0060] <Pressing process> The method of the present disclosure includes (d) pressing the laminate. According to this method, the number of pressing steps can be reduced to one, and therefore the production cost is low. Examples of the pressing method include roll pressing.

[0061] The method of the present disclosure can further include pressing the preliminary lithium alloy layer to obtain a lithium alloy layer. In this manner, the second slurry can be applied onto the densified lithium alloy layer, and the penetration of the LFP into the lithium alloy layer can be suppressed, thereby reducing the frequency of contact between the lithium alloy and the carbon material covering the positive electrode active material.

[0062] The positive electrode active material layer of the present disclosure can also be manufactured by a method other than the above. For example, first, the positive electrode collector is immersed in an electrolyte containing a metal element constituting a lithium alloy, and a lithium alloy layer can be formed on the positive electrode collector by electrolytic plating. Then, similarly to the above, a layer containing a positive electrode active material is formed by going through a coating process of a slurry containing a positive electrode active material, a drying process, and a pressing process, and the positive electrode active material layer of the present disclosure can be manufactured.

[0063] Lithium-ion battery As shown in FIG. 4, the lithium ion battery 1 of the present disclosure has a positive electrode current collector 10, a separator 30, and a positive electrode active material layer 20 of the present disclosure interposed between the positive electrode current collector 10 and the separator 30. That is, the lithium ion battery 1 of the present disclosure has a positive electrode current collector 10, a positive electrode active material layer 20 of the present disclosure, and a separator 30 in this order. The lithium ion battery 1 of the present disclosure may have a positive electrode current collector 10, a positive electrode active material layer 20 of the present disclosure, a separator 30, a negative electrode active material layer 40, and a negative electrode current collector 50 in this order. Note that, although FIG. 4 illustrates an embodiment in which the lithium alloy layer 22 is disposed on the surface on the positive electrode current collector side, the lithium ion battery 1 of the present disclosure is not limited to this embodiment. That is, the lithium alloy may not form a layer, and the lithium alloy or a lithium alloy layer may be disposed on the surface on the separator side.

[0064] The lithium ion battery of the present disclosure may be a liquid battery containing an electrolytic solution as an electrolyte layer, or may be a solid battery having a solid electrolyte layer as an electrolyte layer. The electrolyte layer in the liquid battery may be a separator impregnated with an electrolytic solution. The solid electrolyte layer in the solid battery may have the function of a separator. In the present disclosure, the term "solid-state battery" refers to a battery that uses at least a solid electrolyte as an electrolyte, and therefore the solid-state battery may use a combination of a solid electrolyte and a liquid electrolyte as an electrolyte. The solid-state battery of the present disclosure may also be an all-solid-state battery, i.e., a battery that uses only a solid electrolyte as an electrolyte.

[0065] In the lithium ion battery of the present disclosure, when the battery is initially charged and discharged, lithium ions are released from the lithium alloy, and metal elements that constituted the lithium alloy remain.

[0066] Thus, after an initial charge and discharge, the lithium ion battery of the present disclosure: positive electrode current collector, Separator, and A positive electrode active material layer interposed between the positive electrode current collector and the separator A lithium ion battery having the positive electrode active material layer has a positive electrode active material and a metal element, The positive electrode active material is coated with a carbon material, The alloying potential of the metal element with lithium is 0.5V (vs. Li / Li + ) or more, and the metal element is disposed on a surface of the positive electrode active material layer facing the positive electrode current collector and / or on a surface of the positive electrode active material layer facing the separator; It may be a lithium ion battery.

[0067] <Positive electrode current collector> The positive electrode current collector may be made of a known metal that can be used as a positive electrode current collector for lithium ion batteries. Examples of such metals include metal materials containing at least one element selected from the group consisting of Cu, Ni, Al, V, Au, Pt, Mg, Fe, Ti, Pb, Co, Cr, Zn, Ge, In, Sn, and Zr. The form of the positive electrode current collector is not particularly limited, and may be in various forms such as a foil, a mesh, or a porous form. The positive electrode current collector may be one in which the above metal is vapor-deposited or plated on the surface of a substrate.

[0068] <Cathode active material layer> For the positive electrode active material layer of the present disclosure, the above description regarding the positive electrode active material layer of the present disclosure can be referred to.

[0069] <Separator> The separator may be a known separator used in lithium ion batteries. For example, the separator may be made of a resin such as polyethylene (PE), polypropylene (PP), polyester, or polyamide. The separator may have a single layer structure or a multi-layer structure. As the multi-layer separator, for example, a multi-layer separator made of the above resin, for example, a separator with a two-layer structure of PE / PP, or a separator with a three-layer structure of PP / PE / PP or PE / PP / PE, etc. may be used. The separator may be made of a nonwoven fabric such as a cellulose nonwoven fabric, a resin nonwoven fabric, or a glass fiber nonwoven fabric. The thickness of the separator is not particularly limited, and may be, for example, 5 μm or more and 1 mm or less.

[0070] When the lithium ion battery of the present disclosure is a liquid battery, the separator may be impregnated with an electrolytic solution to form an electrolyte layer.

[0071] (electrolyte) The electrolyte contains a lithium salt and a solvent. Examples of the lithium salt include lithium hexafluorophosphate (LiPF6), lithium tetrafluorophosphate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium trifluoromethanesulfonate (LiCF3SO3), and lithium bis(trifluoromethanesulfonyl)imide (Li(CF3SO2)2N). Examples of the solvent include carbonate esters, cyclic esters (ethylene carbonate (EC), propylene carbonate (PC), etc.), chain esters (dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), etc.), aliphatic carboxylate esters (methyl formate (MF), etc.), γ-lactones (γ-butyrolactone (BL), etc.), chain ethers (1,2-dimethoxyethane (DME), etc.), or solvents that combine some of these. Among these, the solvent may be an aprotic polar organic solvent, or one that contains a cyclic carbonate compound (high dielectric constant, high viscosity) such as EC and a chain carbonate compound such as DEC. The solvent may also be an ionic liquid.

[0072] When the lithium ion battery of the present disclosure is a solid-state battery, the solid electrolyte layer can function as a separator.

[0073] The solid electrolyte layer includes a solid electrolyte. For the solid electrolyte, reference can be made to the above description regarding the positive electrode active material layer of the present disclosure.

[0074] <Negative electrode active material layer> The negative electrode active material layer includes a negative electrode active material, and may optionally include a conductive assistant and a binder. When the lithium ion battery of the present disclosure is a solid-state battery, the negative electrode active material layer may optionally include a solid electrolyte.

[0075] As the negative electrode active material, a known active material may be used. For example, as the negative electrode active material, silicon-based active materials such as silicon, silicon alloys, and silicon oxide; carbon-based active materials such as graphite and hard carbon; various oxide-based active materials such as lithium titanate; metallic lithium, lithium alloys, and the like may be used. Only one type of negative electrode active material may be used alone, or two or more types may be used in combination. The negative electrode active material may be, for example, particulate, and the size thereof is not particularly limited.

[0076] For the conductive assistant, binder, and solid electrolyte, reference can be made to the above descriptions regarding the positive electrode active material layer of the present disclosure.

[0077] <Negative electrode current collector> For the negative electrode current collector, reference can be made to the above description regarding the positive electrode current collector of the present disclosure. EXAMPLES

[0078] Example 1 <Production of Evaluation Cells> (Slurry preparation process) A lithium-bismuth (Li3Bi) alloy as a lithium alloy and a binder were mixed in N-methyl-2-pyrrolidone (NMP) as a first dispersion medium to prepare a first slurry. Lithium iron phosphate (LFP) as an olivine type positive electrode active material coated with a carbon material, a conductive assistant, and a binder were mixed in NMP as a second dispersion medium to prepare a second slurry.

[0079] (First slurry application step, drying step, and pressing step) The first slurry was applied to an aluminum (Al) foil as a positive electrode current collector. Then, the NMP as the first dispersion medium was dried and removed to obtain a preliminary lithium alloy layer. The obtained preliminary lithium alloy layer was pressed to obtain a lithium alloy layer.

[0080] (Second slurry application step, drying step, and pressing step) The second slurry was applied to the lithium alloy layer, and then the NMP serving as the second dispersion medium was dried and removed to obtain a layer, which was then pressed to form a positive electrode active material layer on the positive electrode current collector.

[0081] (Cell manufacturing process) A separator and a negative electrode active material layer containing graphite as a negative electrode active material were laminated on the obtained positive electrode active material layer, and the laminated film was vacuum dried and placed in the laminated film. Further, an electrolyte solution was injected into the laminated film, and the laminated film was sealed to obtain an evaluation cell of Example 1.

[0082] "evaluation" <Charge / Discharge Test> Based on the mass of the positive electrode active material contained in the evaluation cell, the current value at 130 mA / g was defined as 1 C rate, and CCCV charging and discharging was performed at a voltage of 2.2 to 4.1 V, with a charge / discharge current value of 0.2 C and a cut-off current value of 0.03 C. The obtained CCCV capacity was taken as the capacity of the cell.

[0083] Example 2 An evaluation cell of Example 2 was obtained and evaluated in the same manner as in Example 1, except that a lithium-antimony (Li3Sb) alloy was used as the lithium alloy.

[0084] Example 3 An evaluation cell of Example 3 was obtained and evaluated in the same manner as in Example 1, except that a lithium-tin (LiSn) alloy was used as the lithium alloy.

[0085] Comparative Example 1 The Li3Bi alloy, LFP, conductive assistant, and binder were mixed in NMP as a dispersion medium to prepare a slurry. The obtained slurry was applied to an Al foil. Then, the NMP as a dispersion medium was dried and removed, and the obtained layer was pressed to obtain an evaluation cell of Comparative Example 1, which was then evaluated. The Li3Bi alloy and the LFP were mutually dispersed.

[0086] Comparative Example 2 An evaluation cell of Comparative Example 2 was obtained and evaluated in the same manner as in Comparative Example 1, except that a Li3Sb alloy was used as the lithium alloy.

[0087] Comparative Example 3 An evaluation cell of Comparative Example 3 was obtained and evaluated in the same manner as in Comparative Example 1, except that a LiSn alloy was used as the lithium alloy.

[0088] Comparative Example 4 An evaluation cell for Comparative Example 4 was obtained and evaluated in the same manner as in Comparative Example 1, except that no lithium alloy was used.

[0089] The total volume of the positive electrode active material and the lithium alloy contained in the positive electrode active material layer was designed to be the same in all of the examples and comparative examples.

[0090] "result" For the above examples and comparative examples, the LFP content and volume, the thickness of the layer containing LFP, the types and alloying potentials of the metal elements constituting the lithium alloy, the lithium alloy content and volume, and the thickness of the lithium alloy layer are shown in Table 1.

[0091] [Table 1]

[0092] As shown in Table 1, the cells of the examples in which the lithium alloy was disposed on the surface of the positive electrode active material layer facing the positive electrode current collector had larger battery capacities than the cells of Comparative Examples 1 to 3 in which the lithium alloy and the positive electrode active material were mutually dispersed in the positive electrode active material layer, and the cell of Comparative Example 4 in which no lithium alloy was present. [Explanation of symbols]

[0093] 1 Lithium-ion battery 10 Positive electrode current collector 20 Cathode active material layer 21 Layer containing positive electrode active material 21a Cathode active material 22 Lithium alloy layer 22a Lithium Alloy 30 Separator 40 Negative electrode active material layer 50 Negative electrode current collector

Claims

1. A positive electrode active material layer interposed between a positive electrode current collector and a separator, A positive electrode active material and a lithium alloy of lithium and a metal element, The positive electrode active material is coated with a carbon material, The metal element has an alloying potential with lithium of 0.5 V (vs. Li / Li ＋ ) or more, and the lithium alloy is disposed on a surface of the positive electrode active material layer facing the positive electrode current collector and / or a surface of the positive electrode active material layer facing the separator; Cathode active material layer.

2. The positive electrode active material layer according to claim 1 , wherein the lithium alloy forms a lithium alloy layer.

3. The positive electrode active material layer according to claim 2 , wherein the lithium alloy layer has a thickness of 1 μm or more and 20 μm or less.

4. The positive electrode active material layer according to claim 1 , wherein the positive electrode active material is an olivine type positive electrode active material.

5. 5. The positive electrode active material layer according to claim 4, wherein the olivine type positive electrode active material is at least one selected from the group consisting of lithium iron phosphate, lithium manganese iron phosphate, lithium manganese phosphate, and lithium cobalt phosphate.

6. The positive electrode active material layer according to claim 1 , wherein the metal element is at least one selected from the group consisting of bismuth, antimony, and tin.

7. 2 . The positive electrode active material layer according to claim 1 , wherein a ratio of a mass of the positive electrode active material to a mass of the lithium alloy is 3.0 or more and 15.0 or less.

8. 2. The positive electrode active material layer according to claim 1, wherein a thickness of the positive electrode active material layer excluding the lithium alloy is 20 μm or more and 300 μm or less.

9. The positive electrode current collector, The separator, and The positive electrode active material layer according to any one of claims 1 to 8, which is interposed between the positive electrode current collector and the separator. A lithium-ion battery having

10. positive electrode current collector, Separator, and a positive electrode active material layer interposed between the positive electrode current collector and the separator; A lithium ion battery having the positive electrode active material layer has a positive electrode active material and a metal element, The positive electrode active material is coated with a carbon material, The metal element has an alloying potential with lithium of 0.5 V (vs. Li / Li ＋ ) or more, and the metal element is disposed on a surface of the positive electrode active material layer facing the positive electrode current collector and / or a surface of the positive electrode active material layer facing the separator; Lithium-ion battery.

11. A method for producing the positive electrode active material layer according to any one of claims 1 to 8, comprising the following steps: (a) applying a first slurry containing the lithium alloy and a first dispersion medium to a substrate; (b) applying a second slurry containing the positive electrode active material and a second dispersion medium after the step (a); (c) drying and removing the first and second dispersion media to obtain a laminate; and (d) pressing the laminate;

12. The method of claim 11 , wherein the substrate is a positive electrode current collector.

13. 12. The method of claim 11, further comprising, prior to step (b), drying and removing the first dispersing medium to obtain a preliminary lithium alloy layer.

14. The method of claim 13, further comprising pressing the preliminary lithium alloy layer to obtain a lithium alloy layer.

15. The method of claim 11 , wherein the first and second dispersion media are the same dispersion media.

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